The present invention relates to an audio device for motor vehicles, to be carried in an automobile.
Recently, audio devices of this type tend to be made with high precision, and particularly, a car stereo device can provided a reproduced sound of good high frequency range. Also, noise inherent to a tape can be reduced by emplying a noise reduction system such as Dolby or the like. That is, such audio device can reproduce a high frequency range up to 1,500 Hz and improves S/N ratio by a large margin.
When the high precision of such device is improved, however, a slight noise picked up from the outside becomes terribly annoying. Particularly, when increasing the engine power of an automobile, the noise induced by operating an ignition plug is mixed with and introduced in a power source line connected to the battery of an automobile, and led to a car stereo. The noise thus is produced together with the reproduced sound, and spoils the reproduced sound which otherwise is of high quality.
It has until now been difficult to completely remove such noise, and as a countermeasure, a filter is used for cutting out a high frequency range, which is against the tendency to high precision in the aforementioned device.